**6. Nutraceutical oligosaccharides products obtained by diluted thermopressurized phosphoric acid treatment of microalgae cell walls**

Our more recent application of the oPA-mediated catalysis of polymeric sugars has been recently published [64]. The hydrolysis substrates, initially, were microalgae cell walls. This is a very convenient approach to be coupled to microalgae whole biomass once extracted with hot organic solvents (e.g., anhydrous ethanol) to preliminary redeem the lipid material for biodiesel production. In fact, our prospection in these so intensively explored marine unicellular microorganism has gone far: the microalgae (*Chlorella vulgaris*) and cyanobacteria or blue-green algae (*Arthrospira platensis*; formerly *Spirulina platensis*) biomasses, coming from photobioreactors or large open bowls installed in the open roof of local steak house were permanently bubbled with the whole but filtered gases and other volatile components of the hot stream arising from the grills and driven to the bottom of photobioreactors and bowls with the help of a fan. Finalizing, the following chromatographic illustration – variable series of oligosaccharides – confirms the validity of this technology novelty (**Figure 8**).

**Figure 8.** Thin-layer chromatography (TLC) of Nutraceutical oligosaccharides (NOs) arising from diluted thermopressurized oPA-catalyzed treatment of two microalgae and one cyanobacterium cell walls. Real effective pH 2.0 (after equilibration and complete wetting of each microorganism cell mass) and then a thermopressurization at 4.5 atm (156°C) till the peak condition for 2 minutes. Mobile phase: Acetonitrile:Isopropanol:Water (15:3:5). Chromogenic reagent: Orcinol in sulfuric acid. Standards: (Gal A) galacturonic acid, (Rha) rhamnose, (Man) mannose, (Ara) arabinose, (Gal) galactose, (Xyl) xylose, Rf = 0.48 - (Glu) glucose, Rf 0.38 - (Cb) cellobiose and (Mt) maltose, Rf = 0.29 - (Mtt) maltotriose, (XOS) xylo-oligosaccharides, (COS) cello-oligosaccharides, Rf = 0.83 - (HMF) hydroxymethylfurfural. (Source: Authors; picture abstracted from Bruna Leal master dissertation, supervised by Prof. Marcelo R. Prado and Adéia Grzybowski, 2015).
